So he really was toast after all. Ed Miliband's Wednesday jibe had seemed at first to have missed its target. Initial reaction to the Labour leader's Commons call for Andrew Mitchell to quit as chief whip for swearing at the police was that the assault had rallied Conservatives behind David Cameron's newly appointed ally. The toast seemed a little limp on Thursday but as the Westminster week wound down it was clear that the allegations were not being shaken off. On Friday night Mr Mitchell bowed to the pressure, leaving the prime minister with a lost soulmate, an awkward hole to fill in his team, and exactly the sort of autumn embarrassment he could do without. Crisp weekend toast for Mr Miliband then, spread thick with relish.

Conspiracy theorists were inevitably tempted to read a surreal political day in such a way as to argue that Mr Mitchell had been pushed as a desperate ploy to distract attention from this latest gift to Labour. George Osborne's train ticket mixup for travelling first-class on a second-class ticket (and on a railway which had already caused the government grief this autumn) is a metaphor for almost everything that feels wrong about the government at present. Labour must have felt that Christmas had come early. The possibility that Mr Mitchell was quickly sacrificed as a human shield for the chancellor is a seductive thought.

But it was trenchantly denied. Mr Mitchell finally went, it was argued, for old fashioned reasons. He no longer enjoyed the confidence of too many colleagues, not least among the generally pro-Cameron 2010 intake. The Mitchell affair had simply gone on too long and was inflicting too much grief. Mr Osborne has been further weakened all the same.

Mr Mitchell now becomes the fourth member of Mr Cameron's original 2010 cabinet to have been forced to resign against his will. He follows David Laws (since restored to government), Liam Fox and Chris Huhne on to the back benches. Mr Cameron said that he would like to see Mr Mitchell return. But these wishes are more easily stated than fulfilled in modern politics – and Mr Mitchell will not be back soon. The chief whip departed still protesting his innocence – and some of the words in his resignation letter were a first for the genre.

His resignation at the hands of the police leaves a bad taste (as the former Labour MP Chris Mullin argued this week). It may harden hearts between ministers and the police unions. But the practical reality is that Mr Mitchell's position had become almost impossible all the same, especially in the regrettable current climate of contempt towards politicians.

In the end, as Ted Heath once said, a chief whip must always be unheard and invisible. A good whip's work is done out of the spotlight. But the spotlight has been constantly seeking Mr Mitchell out. This made it desperately hard to carry credibility with MPs — crucial in a coalition parliament where all votes matter and the partners are increasingly restive. Mr Mitchell could no longer do that. Mr Cameron will want the new chief whip Sir George Young, the quintessential safe pair of hands as well as a cyclist of calm disposition, to reassert his authority and then keep his feelings towards the police firmly zipped.